/Engine/Source/Runtime/LiveLinkInterface/Public/ILiveLinkClient.h
Whether or not the client has a subject with this name enabled Only 1 subject with the same name can be enabled. At the start of the frame, a snapshot of the enabled subjects will be made. That snapshot dictate which subject will be used for the duration of that frame.
bool IsSubjectEnabled ( [FLiveLinkSubjectName](API\Runtime\LiveLinkInterface\FLiveLinkSubjectName) SubjectName ) const